Mononuclear cell-mediated modulation of synovial cell metabolism. I. Collagen synthesis.

Human PHA-stimulated mononuclear cells produce a factor which inhibits synovial cell collagen and non-collagen protein synthesis, whereas it enhances hyaluronic acid (HA) production. Indomethacin (10(-4)-10(-6) M), a cyclo-oxygenase inhibitor, suppresses this effect, suggesting that the mechanism is prostaglandin-mediated. The active material, of apparent molecular weight 12 000-20 000, also displays the properties of the mononuclear cell factor (MCF) previously described by others, since its stimulates collagenase and PGE2 release by the cultured synovial cells. Furthermore, it co-purifies with interleukin 1 (IL 1) as shown by lymphocyte-activating factor activity. This strongly suggests that IL 1 could be responsible for some (or all) the effects observed on MCF-exposed synovial cells. From these data, we deduce the possibility that mononuclear cells may participate in limiting synovial collagen deposition in rheumatoid arthritis.